I beg to differ; airfare is required by korean law. Korean immigration requires any business that wants to sponsor someone to sign a sponsor form. I have a copy of it. If I can figure out how to post it here, I will. I have a copy of it on a disket. I'll forward it to someone who knows how to post it on this site for all to have.
Anyway...
This sponsor form states that "you are require to pay for housing and return airfare to the home country." If the business, in this case, a school, does not sign the sponsor form, immigratiom will not issue a visa.